The use of natural products as starting materials for the manufacture of various large-scale chemical and fuel products which are presently made from petroleum- or fossil fuel-based starting materials, or for the manufacture of biobased equivalents or analogs thereto, has been an area of increasing importance. For example, a great deal of research has been conducted into the conversion of natural products into fuels, as a cleaner and, certainly, as a more sustainable alternative to fossil-fuel based energy sources.
Agricultural raw materials such as starch, cellulose, sucrose or inulin are inexpensive and renewable starting materials for the manufacture of hexoses, such as glucose and fructose. It has long been appreciated in turn that glucose and other hexoses, in particular fructose, may be converted into other useful materials, such as 5-hydroxymethyl-2-furaldehyde, also known as 5-hydroxymethylfurfural or simply hydroxymethylfurfural (HMF):

The sheer abundance of biomass carbohydrates available provides a strong renewable resource base for the development of commodity chemical and fuel products based on HMF. For example, U.S. Pat. No. 7,385,081, issued in June 2008 to Gong, estimates, for example, that of the approximately 200 billion tons of biomass produced annually, 95% was in the form of carbohydrates, and only 3 to 4% of the total carbohydrates were then used for food and other purposes.
In view of this fact, and due to HMF's various functionalities, it has been proposed that the HMF thus obtainable from hexoses such as fructose and glucose, could be utilized to produce a wide range of products derived from renewable resources, such as polymers, solvents, surfactants, pharmaceuticals, and plant protection agents. HMF has in this regard been proposed, as either a starting material or intermediate, in the synthesis of a wide variety of compounds, such as furfuryl dialcohols, dialdehydes, esters, ethers, halides and carboxylic acids.
A number of the products discussed in the literature derive from the oxidation of HMF or of certain derivatives of HMF, especially, ether and ester derivatives of HMF. One such product, 2,5-furandicarboxylic acid (FDCA, also known as dehydromucic acid), has been discussed as a biobased, renewable analog to terephthalic acid in the production of such multi-megaton polyester polymers as poly(ethylene terephthalate) or poly(butylene terephthalate), as well as a useful monomer for making other commercially valuable polymeric products, for example, in polyamides. FDC A esters have also recently been evaluated as replacements for phthalate plasticizers for PVC, see, e.g., WO 2011/023491A1 and WO 2011/023590A1, both assigned to Evonik Oxeno GmbH, as well as R. D. Sanderson et al., Journal of Appl. Pol. Sci. 1994, vol. 53, pp. 1785-1793.
While FDCA and its derivatives (for example, the ester derivatives just mentioned) have attracted a great deal of recent commercial interest, with FDCA being identified, for instance, by the United States Department of Energy in a 2004 study as one of 12 priority chemicals for establishing the “green” chemical industry of the future, the potential of FDCA (due to its structural similarity to terephthalic acid) to be used in making polyesters, for example, has been recognized at least as early as 1946, see GB 621,971 to Drewitt et al, “Improvements in Polymer”.
Unfortunately, viable commercial-scale processes have proven elusive. A threshold challenge has been the development of a commercially viable process to make an HMF or HMF ester or ether derivative from which FDCA could be prepared. Acid-based dehydration methods have long been known for making HMF, being used at least as of 1895 to prepare HMF from levulose (Dull, Chem. Ztg., 19, 216) and from sucrose (Kiermayer, (Chem. Zig., 19, 1003). However, these initial syntheses were not practical methods for producing HMF due to low conversion of the starting material to product. Inexpensive inorganic acids such as H2SO4, H3PO4, and HCl have been used, but these are used in solution and are difficult to recycle. In order to avoid the regeneration and disposal problems, solid sulfonic acid catalysts have also been used. The solid acid resins have not proven entirely successful as alternatives, however, because of the formation of deactivating humin polymers on the surface of the resins. Still other acid-catalyzed methods for forming HMF from hexose carbohydrates are described in Zhao et al., Science, Jun. 15, 2007, No. 316, pp. 1597-1600 and in Bicker et al., Green Chemistry, 2003, no. 5, pp. 280-284. In Zhao et al., hexoses are treated with a metal salt such as chromium (IT) chloride in the presence of an ionic liquid, at 100 degrees Celsius for three hours to result in a 70% yield of HMF, whereas in Bicker et al., sugars are dehydrocyclized to HMF at nearly 70% reported selectivity by the action of sub- or super-critical acetone and a sulfuric acid catalyst
In the acid-based dehydration methods, additional complications arise from the rehydration of HMF, which yields by-products such as levulinic and formic acids. Another unwanted side reaction includes the polymerization of HMF and/or fructose resulting in humins, which are solid waste products and act as catalyst poisons where solid acid resin catalysts are employed, as just mentioned. Further complications may arise as a result of solvent selection. Water is easy to dispose of and dissolves fructose, but unfortunately, low selectivity and the formation of polymers and humins increases under aqueous conditions.
In consideration of these difficulties and in further consideration of previous efforts toward a commercially viable process for making HMF, Sanborn et al. in US Published Patent Application 2009/0156841A1 (Sanborn et al) describe a method for producing “substantially pure” HMF by heating a carbohydrate starting material (preferably fructose) in a solvent in a column, continuously flowing the heated carbohydrate and solvent through a solid phase catalyst (preferably an acidic ion exchange resin) and using differences in the elution rates of HMF and the other constituents of the product mixture to recover a “substantially pure” HMF product, where “substantially pure” is described as meaning a purity of about 70% or greater, optionally about 80% or greater, or about 90% or greater. An alternative method for producing HMF esters performs the conversion in the presence of an organic acid, which can also serve as the solvent Acetic acid is mentioned in particular as a solvent for fructose. The resulting acetylated HMF product is reported to be “more stable” than HMF, because upon heating HMF is described as decomposing and producing byproducts “that are not easily isolated or removed,” page 4, paragraph 0048.
Further, the acetylated HMF is said to be more easily recovered by distillation or by extraction, though filtration, evaporation and combinations of methods for isolating the HMF esters are also described (page 2, para. 0017). The product, HMF ester which may include some residual HMF, can then be mixed in one embodiment with organic acid, cobalt acetate, manganese acetate and sodium bromide and oxidized to FDCA in the presence of oxygen and at elevated temperatures and pressures. In the examples, a Parr reactor is used for performing the oxidation.
Still other derivatives of HMF have been prepared for subsequent oxidation to FDCA or to the ester derivatives of FDCA, as shown, for example, in U.S. Pat. No. 8,558,018 to Sanborn et al., wherein 5-(alkoxymethyl)furfural (AMF), 5-(aryloxymethyl)furfural, 5-(cycloalkoxymethyl)furfural and 5-(alkoxycarbonyl)furfural compounds are described as oxidized in the presence of dissolved oxygen and a Co(II), Mn(II), Ce(III) salt catalyst or mixtures thereof to provide FDCA and various other related materials. The products that can be made will understandably vary dependent on the starting material or mix of starting materials, but can include 2,5-furandicarboxylic acid (FDCA) with the inclusion of bromide. When the reactant is an ether derivative of HMF, the products are surprisingly ester derivatives where either both the ether and aldehyde functional groups have been oxidized, or just the ether function group may be oxidized producing one or both of 5-ester-furan-2-acids (i.e., 5-alkoxycarbonylfurancarboxylic acids) or 5-ester-furan aldehydes, (i.e., alkoxycarbonylfurfurals a. k. a 5-(alkoxycarbonyl)furfural).
In relation to the second part of a process for making FDCA from carbohydrates via HMF or a suitable HMF derivative, for example, an ether or ester derivative as just described, a number of other references have also proposed an oxidation in the presence of very similar catalyst systems to that proposed in Sanborn et al. Thus, for example, in U.S. Pat. No. 7,956,203 to Grushin et al. (E.I. DuPont de Nemours and Company), furan-2,5-dicarboxylic acid (FDCA) is described as made by contacting an alcohol/aldehyde such as HMF with an oxidant in the presence of a metal bromide catalyst to form a dialdehyde, optionally isolating the dialdehdyde, then contacting the dialdehyde with an oxidant in the presence of a metal bromide catalyst to form an acid/aldehyde, with optionally isolating the acid/aldehyde, and finally contacting the acid/aldehyde with an oxidant in the presence of a metal bromide catalyst to form the diacid. Grushin contemplates carrying out this process in the presence of a solvent or solvent mixture comprising an aliphatic C2-C6 monocarboxylic acid, which is preferably acetic acid.
The metal bromide catalyst used in Grushin's process comprises a soluble transition metal compound and soluble bromine-containing compound. One metal or a combination of two or more metals may be used, with the transition metal component preferably being cobalt and/or manganese, optionally but preferably further comprising zirconium. Each of the metal components (Co, Mn, Zr) can be provided in any of their known ionic or combined forms, with metal acetate tetrahydrates being mentioned as preferred. The source of bromide “can be any compound that produces bromide ions in the reaction mixture”, col. 6, lines 32-33, e.g., hydrogen bromide, hydrobromic acid, sodium bromide, elemental bromine, benzyl bromide, and tetrabromoethane, with sodium and hydrobromic acid being mentioned as preferred.
In U.S. Pat. No. 8,242,292 to Yutaka et al. (Canon Kabushiki Kaisha), a similar method is described for producing FDCA, wherein yield improvements are attributed to the regulation of water content in the oxidation process. HMF is again brought into contact with an oxidant in an organic acid solvent in the presence of bromine and a metal catalyst while removing water produced by the reaction. The metal catalyst preferably contains Co or Mn, but more preferably contains both of Co and Mn, while Br is described as serving as an initiator for the reaction and as advancing the reaction while reducing Co as a main oxidation catalyst through ion discharge. The manner in which bromine is introduced is not addressed by Tutaka et al., but each of the examples employs sodium bromide.
U.S. Pat. No. 8,519,167 to Mufoz de Diego et al. (Furanix Technologies B V) describes a method for the preparation of FDCA and/or an alkyl ester of FDCA through contacting a feed comprising a starting material selected from 5-alkoxymethylfurfural, 2,5-di(alkoxymethyl)furan and a mixture thereof, and optionally further containing HMF, with an oxidant in the presence of an oxidation catalyst comprising at least one of cobalt and manganese (and preferably containing both) as well as a source of bromine, preferably a bromide. The bromine source is described essentially as in Grushin, as including any compound that produces bromide ions in the reaction mixture, with hydrobromic acid and/or sodium bromide being preferred. The starting materials are described as prepared from carbohydrates, then through isolation of a feed for contact with the oxidant.
U.S. Pat. No. 8,791,278 to Shaikh et al. (Eastman Chemical Company) describes a process for making FDCA and/or a dry purified FDCA through oxidizing at least one oxidizable compound in an oxidizable raw material stream in the presence of an oxidizing gas stream, solvent stream and at least one catalyst system. The catalyst system is described as preferably comprised of at least one selected from, but not being limited to, cobalt, bromine and manganese compounds which are soluble in the selected oxidation solvent. The bromine component may be added as elemental bromine, in combined form, or as an anion. “Suitable” sources of bromine include hydrobromic acid, sodium bromide, ammonium bromide, potassium bromide, and tetrabromoethane, with hydrobromic acid and sodium bromide again listed as preferred (as in each of Grushin, Yutaka and Shaikh).
Those familiar with the manufacture of terephthalic acid will be very familiar with the use of such solvent-soluble Co/Mn/Br catalyst systems as taught in the several references just summarized. Metal bromide catalysts employing Co and Mn, and in some cases additional metals such as Zr and/or Ce, have been widely commercially used for the liquid-phase oxidation of para-xylene to terephthalic acid. While there has been some limited work done on alternative catalyst systems for converting HMF (and/or an HMF derivative, e.g, an HMF ether or ester derivative) to FDCA, yet because the HMF to FDCA conversion has been evaluated with the overall objective in mind of making a renewable analog to terephthalic acid, it is perhaps not surprising that the catalysts proposed for use in most of the HMF/HMF derivative to FDCA art, as well as the general reaction parameters and process steps described therein, mirror or at least are strongly correlated to the p-xylene oxidation art. There would be distinct and obvious advantages to a manufacturer's developing and implementing an HMF/HMF derivative to FDCA oxidation technology that closely resembles the existing p-xylene to terephthalic acid oxidation technology that has been so widely used, including, but not being limited to, easing the transition for operations personnel accustomed to the p-xylene process, making use of longstanding catalyst supply relationships and facilitating the use of excess terephthalic acid-manufacturing capacity and associated depreciated capital assets.
However, there is a need for a new, more efficient and more cost effective process that converts sugars to furandicarboxylic acid (FDCA) and/or valuable derivatives thereof, for example, diether, diester, ether-acid, ether-ester, ester-acid, ester-aldehyde, ether-aldehyde, ether-acetal, ester-acetal, acetal-acid, alcohol-acid, alcohol-ester, alcohol-acetal, diol, diacetal and aldehyde-acetal derivatives, that can be used as monomers in polymeric syntheses or as intermediates in other syntheses.